ALBERT

Description: Background: R/R DLBCL remains an area of unmet medical need and treatments with novel mechanisms of action are urgently needed. Germinal center DLBCLs depend on the histone methyltransferase EZH2 to perpetuate a less-differentiated state and EZH2 activating mutations may be oncogenic drivers in a subset of patients (pts). Inhibition of EZH2 reprograms abnormal cell growth, leading to cell death or differentiation, and subsequent tumor regression. Tazemetostat, a potent, selective, oral EZH2 inhibitor has shown antitumor activity in a phase 1 study that included DLBCL pts with mutated (mt) or wild type (wt) EZH2 tumors, which provides rationale for further investigation of its single agent activity. This open-label, multicenter phase 2 study is evaluating tazemetostat in pts with either mt or wt EZH2 R/R DLBCL or follicular lymphoma (Grade 1-3b); results of an interim analysis of DLBCL pts treated with tazemetostat, as monotherapy or in combination with prednisolone are presented. Methods: Key inclusion criteria include: age ≥18 years, ≥2 prior treatment regimens, and measurable disease. Tazmetostat 800 mg is administered orally, twice daily (BID); prednisolone (40 mg/m2) on days 1 to 5 and days 15 to 19 in a 28-day cycle for 16 weeks. Response was assessed every 8 weeks using IWG-NHL assessment criteria (Cheson 2007). Tumor tissue was analyzed for EZH2 hot spot activating mutations (Y646X, A682G, A692V) using a cobas® EZH2 Mutation Test (Roche Molecular Systems; investigational use only). Hans algorithm was used to determine cell of origin. The primary endpoint is overall response rate (ORR). Secondary endpoints include progression-free survival (PFS), duration of response (DOR) and safety/tolerability. Results: As of May 1, 2018, interim phase 2 safety and activity data were summarized from 226 DLBCL pts (intent to treat analysis). Demographic and clinical activity information are provided in the table, including ORRs of 17% in both mt and wt arms and 9% in the prednisolone arm. Notably, DOR was substantially greater in the mt arm. Safety analysis showed that treatment-emergent adverse events (TEAE) leading to study drug discontinuation or withdrawal from study occurred in 12% of pts. Grade ≥3 treatment-related AEs were reported in 27% of pts. The most common (≥10%) TEAEs (all grades) were: thrombocytopenia (20%), nausea (17%), anemia (15%), neutropenia (15%), vomiting (15%), cough (14%), diarrhea (12%), fatigue (12%), pyrexia (12%), abdominal pain (11%) and asthenia (10%). Conclusion: Tazemetostat was generally well tolerated at a dose of 800 mg BID, as monotherapy or in combination with prednisolone. In this difficult to treat, heavily pretreated, refractory patient population, clinical activity was observed in approximately 20% of monotherapy pts, regardless of mutational status, many of whom had received multiple prior lines of therapy. Tazemetostat in combination with prednisolone did not result in improved activity compared with tazemetostat monotherapy. Disclosures Ribrag: Servier, Pharmamar, Nanostring, Gilead, Infinity, BMS, MSD, Epizyme: Consultancy; Roche: Other: Travel, expenses, accommodation; ESAI: Honoraria, Research Funding. Morschhauser:Epizyme: Consultancy; Roche/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees. McKay:Epizyme: Consultancy, Honoraria. Salles:Roche, Jannsen, Gilead, Celgene, Novartis, Amgen, BMS, Merck, Servier: Honoraria. Tilly:Roche: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria; Astra-Zeneca: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees. Cartron:Sanofi: Honoraria; Roche: Consultancy, Honoraria; Gilead Sciences: Honoraria; Janssen: Honoraria; Celgene: Consultancy, Honoraria. Gribben:Unum: Equity Ownership; Novartis: Honoraria; TG Therapeutics: Honoraria; Abbvie: Honoraria; Medical Research Council: Research Funding; Janssen: Honoraria, Research Funding; Roche: Honoraria; NIH: Research Funding; Wellcome Trust: Research Funding; Cancer Research UK: Research Funding; Pharmacyclics: Honoraria; Kite: Honoraria; Acerta Pharma: Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Dickinson:GSK: Consultancy. Opat:Roche, Celgene, Mundipharma, Janssen: Honoraria; Roche, Celgene, Mundipharma, Janssen: Consultancy. Adib:Epizyme: Employment, Equity Ownership. Blakemore:Epizyme: Employment, Equity Ownership. Larus:Epizyme: Employment, Equity Ownership. Johnson:Zenyaku Kogyo: Other: Travel, accommodations, expenses; Eisai: Research Funding; Incyte: Consultancy; Genmab: Consultancy; Kite: Consultancy; Boeringher Ingelheim: Consultancy; Epizyme: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Research Funding; Celgene: Honoraria; Novartis: Honoraria; Takeda: Honoraria, Travel, accommodations, expenses; Bristol-Myers Squibb: Honoraria.

Description: Introduction: B-cell malignancies may depend on the histone methyltransferase EZH2 to perpetuate a less differentiated state, with activating mutations of EZH2 being potential oncogenic drivers. Tazemetostat, a potent, selective EZH2 inhibitor, is in phase 2 clinical development in relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL). Objective responses were observed in patients (pts) with EZH2 mutant or wild type tumors in the phase 1 part of the phase 1/2 study. The ongoing phase 2 study is enrolling pts with mutant or wild type EZH2 having R/R diffuse large B-cell lymphoma (DLBCL) or follicular lymphoma (FL) to determine efficacy and safety. The primary endpoint is overall response rate. Here we report results of an updated molecular analysis of archived tumor and circulating tumor DNA (ctDNA) collected from pts plasma and associations with preliminary response data, including the discovery of novel candidate molecular predictors of tazemetostat response. Methods: Archived tumor and/or plasma-derived ctDNA samples were obtained during screening from R/R DLBCL and FL pts enrolled to the phase 2 trial of tazemetostat in NHL (NCT01897571). Next generation sequencing was performed retrospectively on archived tumor DNA (target coverage of 1,500X) and ctDNA (20,000X for somatic mutations and 5,000X for structural alterations). DNA was isolated from archived tumor and was tested across a panel of approximately 200 genes, including 62 genes commonly altered in NHL to identify somatic mutations, amplifications, and translocations. The ctDNA sequencing was restricted to the 62 gene NHL panel. Best objective overall response data (Cheson 2007) as of May 1, 2018 were used to generate two groups: responders (R = CR + PR), and non-responders (NR = progressive disease, stable disease, or unknown clinical response). Fisher's exact test (two tailed) was performed to identify DNA variants associated with either the R or NR groups for FL+DLBCL combined and for each NHL sub-type independently (Table 1). All gene associations met an unadjusted P-value threshold of ≤ 0.1. Results: In the combined analysis for all NHL pts, EZH2, BRCA2, ETV6, IKZF3 and TNFRSF14 mutations were associated with clinical response. Eleven genes, including BCL6, BCL2, TP53, PIM1, HIST1H1B and HIST1H1E, mutations were associated with a lack of response to tazemetostat. Association of detection of mutations in EZH2, BCL6 and HIST1H1E and response were detected in both ctDNA and archived tumor analysis, with all other genes achieving P ≤ 0.1 in either the ctDNA or the archived tumor analysis. Analysis of the NHL subcategories revealed in FL that mutations in EZH2 and STAT6 were associated with clinical response while mutations in BCL2, TNFAIP3, FOXO1 and MYD88 were identified as negative predictors. EZH2 was the only gene identified in both the ctDNA and archived tumor analyses in FL. In DLBCL, while EZH2 was not detected as a predictor of response to tazemetostat at P ≤ 0.1, the number of pts with mutant rather than wild type EZH2 was higher in responders than non-responders in both analyses. Positive predictors of tazemetostat response were detected in DLBCL: MYD88, MEF2B, ETV6, MLH1, RECQL4, and RNF43. Negative predictors of response were also identified in DLBCL: BCL2, PDL1, PDL2 and SOCS1. When the genes identified as associated with tazemetostat response in DLBCL were compared between the archived tumor and ctDNA analyses, no genes in common were identified. Conclusions: These analyses confirm genes previously described as potential predictors of tazemetostat response in analyses using smaller patient numbers and less mature clinical response data such as STAT6, EZH2, MYD88, TP53,BCL2, BCL6, PIM1 and HIST1H1E. In addition, identification of PDL1/PDL2 and RECQL4/MLH1/BRCA2 as novel predictors points to potential relevance of immune checkpoint and DNA damage repair pathways as additional pathways that may be of relevance to tazemetostat response in NHL. Subanalyses performed independently on each NHL subtype revealed disease specific biomarkers of response that may point to differences in the factors that can influence response to tazemetostat in DLBCL and FL. Disclosures McDonald: Epizyme: Employment, Equity Ownership. Thomas:Epizyme: Employment, Equity Ownership. Daigle:Epizyme: Employment, Equity Ownership. Morschhauser:Epizyme: Consultancy; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees. Salles:Morphosys: Honoraria; Servier: Honoraria; Janssen: Honoraria, Other: Advisory Board; Takeda: Honoraria; Pfizer: Honoraria; Servier: Honoraria, Other: Advisory Board; Merck: Honoraria; BMS: Honoraria, Other: Advisory Board; Gilead: Honoraria, Other: Advisory Board; Amgen: Honoraria; Epizyme: Honoraria; Acerta: Honoraria; Abbvie: Honoraria; Celgene: Honoraria, Other: Advisory Board, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria. Ribrag:Servier, Pharmamar, Nanostring, Gilead, Infinity, BMS, MSD, Epizyme: Consultancy; ESAI: Honoraria, Research Funding; Roche: Other: Travel, expenses, accommodation. McKay:Epizyme: Consultancy, Honoraria. Tilly:Astra-Zeneca: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees. Johnson:Kite: Consultancy; Genmab: Consultancy; Incyte: Consultancy; Zenyaku Kogyo: Other: Travel, accommodations, expenses; Bristol-Myers Squibb: Honoraria; Eisai: Research Funding; Takeda: Honoraria, Travel, accommodations, expenses; Boeringher Ingelheim: Consultancy; Epizyme: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Research Funding; Celgene: Honoraria; Novartis: Honoraria. Dickinson:GSK: Consultancy. Opat:Roche, Celgene, Mundipharma, Janssen: Honoraria; Roche, Celgene, Mundipharma, Janssen: Consultancy. Jurczak:Gilead: Consultancy; Morphosys: Research Funding; Roche: Research Funding; Servier: Research Funding; TG Therapeutics: Research Funding; Merck: Research Funding; Pharmacyclics: Research Funding; European Medicines Agency: Consultancy; AstraZeneca/Acerta: Consultancy, Research Funding; Sandoz-Nowartis: Consultancy; Afimed: Research Funding; BeiGene: Research Funding; Celgene: Research Funding; Epizyme: Research Funding; Gilead: Research Funding; Janssen: Research Funding; Nordic Nanovector: Research Funding; Janssen: Consultancy. Cartron:Gilead Sciences: Honoraria; Celgene: Consultancy, Honoraria; Janssen: Honoraria; Sanofi: Honoraria; Roche: Consultancy, Honoraria. Zinzani:Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees; Celltrion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees; MSD: Honoraria, Speakers Bureau; Astra Zeneca: Speakers Bureau; Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; SERVIER: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Assouline:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Research Funding, Speakers Bureau; Novartis: Research Funding; Roche: Honoraria, Research Funding, Speakers Bureau. Radford:BMS: Consultancy, Speakers Bureau; Seattle Genetics: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Pfizer: Research Funding; Celgene: Research Funding; Takeda: Consultancy, Research Funding, Speakers Bureau; GlaxoSmithKline: Equity Ownership; AstraZeneca: Equity Ownership; ADC Therapeutics: Consultancy, Research Funding. Gribben:Novartis: Honoraria; Medical Research Council: Research Funding; Acerta Pharma: Honoraria, Research Funding; Roche: Honoraria; Abbvie: Honoraria; Cancer Research UK: Research Funding; Kite: Honoraria; NIH: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Honoraria, Research Funding; TG Therapeutics: Honoraria; Pharmacyclics: Honoraria; Unum: Equity Ownership; Wellcome Trust: Research Funding. Haioun:Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Sciences: Consultancy, Honoraria; Gilead Sciences: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Roche: Consultancy, Honoraria. Le Gouill:Roche: Consultancy, Honoraria; Janssen-Cilag: Consultancy, Honoraria. Clawson:Epizyme: Employment, Equity Ownership. Larus:Epizyme: Employment, Equity Ownership. Blakemore:Epizyme: Employment, Equity Ownership.

Description: Introduction: Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) result in recruitment of another HMT, DOT1L, to a multi-protein complex. This leads to abnormal methylation of Histone H3 lysine 79 (H3K79) at MLL target genes and enhanced expression of leukemogenic genes such as HOXA9 and MEIS1 ( Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and 〉37,000 fold selectivity against non-MLL HMTs. Pinometostat treatment of MLL-rearranged cells and xenografts reduced histone H3K79 methylation, decreased MLL target gene expression, and induced selective leukemia cell kill (Daigle, 2013). We report the safety, activity, pharmacokinetics (PK) and pharmacodynamics (PD) in the phase 1 trial of pinometostat in adult patients (pts) with relapsed/refractory (R/R) leukemia. Methods: This open label dose escalation/expansion study of pinometostat enrolled pts 〉18 years (yrs) with R/R leukemia (NCT01684150). In the dose-escalation phase, pts with AML, ALL, mixed lineage leukemia (MLL), myelodysplastic syndrome, myeloproliferative neoplasm or chronic myeloid leukemia were eligible. Eligibility in the two expansion cohorts: 90 mg/m2 (n = 17) and 54 mg/m2 (n = 6), was restricted to pts with MLL-r or MLL-partial tandem duplication (MLL-PTD). Pinometostat was given via continuous intravenous infusion (CIV) for 21 of 28 day cycles in the dose escalation phase and CIV for 28 of 28 day cycles in the expansion phases, until disease progression or unacceptable toxicity. All pts underwent serial collection of PK and peripheral blood mononuclear cells (PBMC) for PD. Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for dimethylation of H3K79 (H3K79-me2) by ChIP-Seq. Results: As of 28-June-2015, 49 pts have enrolled in the dose escalation and expansion phases. Pts receiving 21/28 day infusions: 12 (n=1), 24 (n=5), 36 (n=4), 54 (n=6) and 80 mg/m2/day (n=3). Pts receiving 28/28 day infusions: 54 (n=6) and 90 mg/m2/day (n=24). Table 1. Patient Characteristics n (%) Median age, yrs (range) 51 (19 - 81) Sex (M / F) 27/22 Diagnosis MLL-r* 29 (59) AML MLL-PTD** 5 (9) MLL-wt 7 (14) ALL MLL-r* 5 (10) MLL-wt 1 (2) MLL MLL-r 1 (2) CMML MLL-r 1 (2) # of prior therapeutic regimens 1 - 2 29 (59) 3 - 4 18 (36) 〉4 2 (4) Prior allogeneic hematopoietic cell transplant 20 (41) * centrally confirmed by karyotype/FISH ** centrally confirmed by NGS (next generation sequencing) Adverse events (AEs) reported in 〉15% of pts regardless of attribution were: nausea, constipation, vomiting, abdominal pain, diarrhea, hypocalcemia, hypokalemia, hypomagnesemia, fatigue, fever, peripheral edema, mucositis, febrile neutropenia, leukocytosis, anemia, cough, dyspnea, and pneumonia. Grade ≥3 non-hematologic related toxicities include: hypophosphatemia (n=1), decreased ejection fraction (n=3), or elevated transaminases (n=1). Nine patients had leukocytosis (absolute monocyte and neutrophil 50% above baseline and above upper limit of normal) or differentiation. The median days of pinometostat treatment was 35 days (range 3-189 days). To date, objective responses observed are morphologic CR (1 pt), cytogenetic CR (MLL negative by FISH) (1 pt), PR (1 pt) and resolution of leukemia cutis (3 pts). Dose proportional PK was observed with rapid attainment of steady-state plasma concentrations (Css) on Day 1 of treatment. Plasma Css correlated with inhibition of global H3K79-me2 in PBMCs. H3K79-me2 ChIP-Seq demonstrated pinometostat induced reductions in methylation at MLL -r target genes HOXA9 and MEIS1 (median inhibition = 61%: range = 13-91%) in all 9 pts analyzed to date from the 90 mg/m2 expansion cohort. Inhibition of H3K79-me2 in leukemic blasts is consistent with DOT1L suppression. PK-PD relationships in both expansion cohorts using both free and total plasma Css are being explored. Conclusions: Pinometostat administered as a CIV to adults with R/R leukemia has an acceptable safety profile. Clinical activity as demonstrated by both marrow responses and resolution of leukemia cutis were observed. In addition, analysis of H3K79-me2 by ChIP-Seq demonstrated PD reductions in the methylation of MLL-r target genes following pinometostat exposure, as expected from DOT1L inhibition. Relationships between PK exposure, reductions in pinometostat induced H3K79-me2 levels and clinical response are being interrogated. Disclosures Stein: Seattle Genetics: Consultancy; Agios Pharmaceuticals: Consultancy. Rizzieri:Teva: Other: ad board, Speakers Bureau; Celgene: Other: ad board, Speakers Bureau. Berdeja:Novartis: Research Funding; Takeda: Research Funding; BMS: Research Funding; Curis: Research Funding; MEI: Research Funding; Abbvie: Research Funding; Onyx: Research Funding; Array: Research Funding; Janssen: Research Funding; Celgene: Research Funding; Acetylon: Research Funding. Altman:Novartis: Other: Advisory board; Spectrum: Other: Advisory board; Ariad: Other: Advisory board; Seattle Genetics: Other: Advisory board; BMS: Other: Advisory board; Astellas: Other: Participation in an advisory board December 2013. Thomson:Epizyme, Inc: Employment. Blakemore:Epizyme: Employment. Daigle:Epizyme, Inc: Employment. Fine:Epizyme: Employment. Waters:Epizyme, Inc: Employment. Armstrong:Epizyme, Inc: Consultancy. Ho:Epizyme, Inc: Employment.

Description: Introduction: MLL-rearranged (MLL-r) acute leukemia in children is characterized by young age at presentation and a poor overall prognosis despite multi-agent chemotherapy. Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) recruit another HMT, DOT1L, to a multi-protein complex leading to aberrant methylation of histone H3 lysine 79 (H3K79) at MLL target genes. This results in enhanced expression of critical genes for hematopoietic differentiation, including HOXA9 and MEIS1, and has been established as a key mechanism for leukemogenesis in MLL-r leukemias (Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and 〉37,000 fold selectivity against non-MLL HMTs. Treatment of MLL-rearranged cells and xenograft models with pinometostat led to reduced histone 3 lysine 79 methylation (H3K79me2), decreased MLL target gene expression and selective leukemia cell kill (Daigle, 2013). Here we report the final results of the pinometostat phase 1 trial in children with relapsed/refractory (R/R) MLL-r acute leukemia. Methods: An open label dose escalation study of pinometostat was performed in patients (pts) aged 3 months to 18 years (yr) with R/R MLL-r leukemia (NCT02141828). Pinometostat was administered via continuous intravenous infusion (CIV) until disease progression or unacceptable toxicity. Pts were assigned to one of two aged-based dose escalation schemas developed from simulations of pediatric exposures using a previously reported physiologically-based PK (PBPK) model (Waters, 2014). All patients underwent serial collection of PK and peripheral blood mononuclear cells (PBMC). Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for H3K79me2 levels by ChIP-Seq. Results: 18 pts were enrolled on study with 9 pts dosed at 70 mg/m2/day and 7 pts at 90 mg/m2/day in the older age cohort (1 to 18 yr) plus 2 pts dosed at 45 mg/m2/day in the younger age cohort (20% of pts were: febrile neutropenia; anemia; leukopenia; thrombocytopenia; hypokalemia; respiratory failure; lymphopenia; neutropenia. Drug-related TEAEs reported in 〉15% of pts were: anemia; thrombocytopenia; leukopenia; rash; lymphopenia; hypocalcemia; hypophosphatemia; neutropenia; ALT elevation; nausea; vomiting. Dose-limiting toxicities (DLT) were: apnea (70 mg/m2); elevated transaminases (2 at 90 mg/m2) in the 〉1 year of age cohort, thus defining 70 mg/m2 as the recommended phase 2 dose (RP2D) in older pts. A RP2D was not determined in pts 〈 1 year of age. Median duration of treatment was 23 days (range 7- 53 days). Pinometostat induced transient decreases in peripheral or marrow leukemic blasts in 7/18 pts, however, these reductions did not meet formal thresholds for objective response. Adjusted mean plasma pinometostat concentrations during the infusion in children 〉1 yr at 70 and 90 mg/m2/d doses (1151 ng/mL) was comparable to mean steady-state concentrations observed in adult patients at the 80 mg/m2/d and 90 mg/m2/d doses (1320 ng/mL and 1410 ng/mL, respectively) and was within the range of 1000-1600 ng/mL at 90 mg/m2/d in ≥ 1 yr predicted by earlier PBPK modeling results. CSF concentrations of pinometostat were below the lower limit of quantification of 1 ng/mL (n = 8) or very low (〈 12 ng/mL) (n = 4), suggesting negligible CSF exposure. H3K79me2 ChIP-Seq on leukemic blasts demonstrated that pinometostat induced reductions in methylation at MLL-r target genes (e.g. HOXA9 and MEIS1) of ≥ 80 % at all post dose time points (15 and 28 days) and doses (70 & 90 mg/m2) tested consistent with DOT1L inhibition. Conclusions: In pediatric pts with R/R MLL-r pinometostat has an acceptable safety profile with a RP2D defined as 70 mg/m2 CIV in children 〉 1 yr. Pinometostat dose/exposure relationships were comparable between adults and children 〉 1 yr. Pharmacodynamic evidence of DOT1L inhibition was observed in leukemic blasts. Transient reductions in peripheral or bone marrow blasts were detected in ~40 % of pts, however no objective responses were observed. Based on the biological activity observed and evidence of combination benefit of pinometostat with standard of care and novel agents in preclinical MLL-r models (Daigle 2015 and Klaus 2015) further clinical investigation of pinometostat combinations is warranted. Figure Figure. Disclosures O'Brien: Seattle Genetics: Research Funding; Celgene: Other: travel expenses for required site investigator meeting, October 2015;; steering committee member for pediatric AML trial, Research Funding; Epizyme: Research Funding; Amgen: Other: participated in one pediatric advisory board for blinatumomab in May 2015, paid consultant fee and travel expenses, Research Funding. Blakemore:Epizyme: Employment. Daigle:Epizyme: Employment. Suttle:Epizyme: Employment. Armstrong:Epizyme, Inc: Consultancy; Vitae Pharmaceuticals: Consultancy; Imago Biosciences: Consultancy; Janssen Pharmaceutical: Consultancy. Ho:Epizyme: Employment, Equity Ownership.

Description: Introduction: MLL-rearranged (MLL-r) acute leukemia in children is characterized by young age at presentation and a poor overall prognosis despite multi-agent chemotherapy. Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) recruit another HMT, DOT1L, to a multi-protein complex leading to aberrant methylation of histone H3 lysine 79 (H3K79) at MLL target genes. This results in enhanced expression of critical genes for hematopoietic differentiation, including HOXA9 and MEIS1, and has been established as a key mechanism for leukemogenesis in MLL-r leukemias (Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and 〉37,000 fold selectivity against non-MLL HMTs. Treatment of MLL-rearranged cells and xenograft models with pinometostat led to reduced histone 3, lysine 79 (H3K79) methylation, decreased MLL target gene expression and selective leukemia cell kill (Daigle, 2013). We report the preliminary safety, pharmacokinetics (PK), pharmacodynamics (PD) and target inhibition in leukemia cells of pinometostat in a phase 1 trial in children with relapsed/refractory (R/R) MLL-r acute leukemia. Methods: An open label dose escalation study of pinometostat was performed in patients (pts) aged 3 months to 18 years (yr) with R/R MLL-r leukemia (NCT02141828). Pinometostat was administered via continuous intravenous infusion until disease progression or unacceptable toxicity. Pts were assigned to one of two aged-based dose escalation schemas developed from simulations of pediatric exposures using a previously reported physiologically-based PK (PBPK) model (Waters, 2014). All patients underwent serial collection of PK and peripheral blood mononuclear cells (PBMC) for PD. Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for di-methylation of H3K79 (H3K79-me2) by ChIP-Seq. Results: As of 28-June-2015, 11 pts have enrolled in the dose escalation of the study consisting of 10 pts (6 pts at 70 mg/m2/day, 4 pts at 90 mg/m2/day) in the older age cohort (1 to 18 yr) and 1 pt (45 mg/m2/day) in the younger age cohort (10 1 (9) Prior allogeneic hematopoietic cell transplant 6 (54) Adverse events (AEs) reported in 〉3 pts regardless of attribution were: anemia, febrile neutropenia, abdominal pain, diarrhea, nausea, vomiting, pain, grade 1 prolonged QTcF, lymphopenia, thrombocytopenia, leukopenia, hypocalcemia, hypokalemia, hypophosphatemia, pleural effusion, respiratory failure, dry skin, rash and hypertension. Grade ≥3 related non-hematologic toxicities include: apnea (n=1 and the only protocol defined dose limiting toxicity), organizing pneumonia (n=1), anorexia (n=1), and febrile neutropenia (n=1). The median duration of treatment was 26 days (range 7- 53 days). Updated response data will be provided. Steady-state plasma concentrations (Css) of pinometostat in children 〉1 yr at 70 and 90 mg/m2 doses were comparable to that observed in adult patients at equivalent doses and were in the range of 800 - 1600 ng/mL, corroborating earlier PBPK modeling results (projected Css range of 1000-1600 ng/mL at 90 mg/m2/d in ≥1 yr). Steady-state CSF concentrations of pinometostat were low ( 1 yr. Analysis of H3K79-me2 ChIP-Seq data demonstrated PD reductions in methylation of MLL-r target genes expected from DOT1L inhibition. Enrollment and dose escalation continue. Disclosures O'Brien: Seattle Genetics, Inc.: Research Funding. Pauly:Seattle Genetics, Inc.: Research Funding. Whitlock:Amgen: Honoraria. Thomson:Epizyme, Inc: Employment. Blakemore:Epizyme: Employment. Daigle:Epizyme, Inc: Employment. Pimentel:Epizyme, Inc: Employment. Waters:Epizyme, Inc: Employment. Armstrong:Epizyme, Inc: Consultancy. Ho:Epizyme, Inc: Employment.

Description: Key Points Pinometostat demonstrates first evidence of DOT1L target inhibition and clinical responses in a subset of MLL-r advanced leukemia patients. The observed safety profile of pinometostat shows potential for exploration of combination therapies in leukemia.

Description: Introduction: The histone methyl transferase EZH2 is the catalytic subunit of the polycomb repressive complex 2 (PRC2) and responsible for methylation of lysine 27 of histone H3 (H3K27), a modification of DNA associated with repressed transcription when trimethylated (H3K27me3). Aberrant EZH2 activity has been implicated as an oncogenic driver in non-Hodgkin's lymphoma (NHL). Here we report the phase 1 first-in-human experience to date with tazemetostat in patients (pts) with NHL. Methods: Tazemetostat was administered orally twice daily (BID) to subjects in five dose cohorts (100 mg [n=6], 200 mg [n= 3], 400 mg [n=3], 800 mg [n=14], 1600 mg [n=12], and one food effect cohort (400 mg [n=7]). Tumor response assessments were performed every 8 weeks. Archival tumor tissue from NHL pts was analysed for EZH2 hot spot mutations Y646X, A682G and A692V (by either amplicon-based next generation sequencing [NGS] or cobas ® EZH2 Mutation Test [in development]), and for additional somatic mutations by NGS focusing on a panel of 39 genes commonly mutated in NHL. In addition, cell-of-origin in Diffuse Large B-cell Lymphoma (DLBCL) patients was determined by immunohistochemistry on archival tumor tissue using the Hans algorithm (Blood, 2004). Results: As of 9-July 2015, 45 pts were enrolled to this trial (CT.gov: NCT01897571). To date 19 NHL pts: 13 DLBCL, 5 follicular lymphoma (FL) and 1 marginal zone lymphoma (MZL) were enrolled. Results to date on the 26 solid tumor pts have been reported separately (ECC, 2015). Adverse events (AE) occurring in 〉10% of the 45 pts regardless of attribution were: asthenia, anorexia, constipation, nausea, dysgeusia, vomiting and muscle spasms with 5 grade 3 or greater related AE's: thrombocytopenia, neutropenia, hypertension, anorexia and transaminase elevation. The median age of the NHL patients enrolled was 62 yrs (range 23-82) and 74% of pts were male. Of the fifteen evaluable NHL pts, objective responses were seen in: 5/9 DLBCL, 3/5 FL and 1/1 MZL. The majority of objective responses occurred at the Recommended Phase 2 Dose of 800 mg BID. EZH2 status in patient tumors was determined for 14/19 NHL patients (n=3 data pending, n=2 tissue unavailable) with 13/14 found to be wild-type (WT) and one patient, who experienced an ongoing PR at week 16, expressing an Y646H mutation. Updated data including duration of response will be presented. In addition, 10/13 patients had evidence of somatic mutations in 〉1 non-EZH2 genes among the 39 genes tested (allelic frequency 〉10% with coverage 〉1000X) known to be commonly mutated in NHL, e.g. MYD88 & CARD11, or involved in epigenetic signalling, e.g. EP300 & CREBBP. Table.Relapsed or refractory NHLTotal(n=19)Evaluable(n=15)Best Response CR+PRaBest Response SDaDLBCLGCB4220Non-GCB6520undetermined3210FL5531MZL1110aper IWG (Cheson, 2007), complete response (CR), partial response (PR), stable disease (SD) Conclusions: Tazemetostat demonstrates a safety profile favorable for chronic dosing and objective responses in pts with either EZH2 WT or mutant B-cell lymphoma, including both GCB and non-GCB sub-types of DLBCL. EZH2 pathway genes and genes commonly somatically mutated in lymphoma are under investigation to elucidate the mechanisms and biomarkers of clinical response to tazemetostat. Based upon the observed safety and efficacy profile of tazemetostat, a phase 2 trial in relapsed or refractory DLBCL and FL pts, stratified by cell-of-origin and EZH2 mutation status, is enrolling. Disclosures Ribrag: Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Eisai: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; Pharmamar: Honoraria, Membership on an entity's Board of Directors or advisory committees. Thomson:Epizyme, Inc: Employment. Keilhack:Epizyme: Employment, Equity Ownership. Blakemore:Epizyme: Employment. Reyderman:Eisai: Employment. Kumar:Eisai: Employment. Fine:Epizyme: Employment. McDonald:Epizyme: Employment. Ho:Epizyme, Inc: Employment.